I am a chaospvp veteran (been here since the first reset) and I know what went wrong the first time.
the outside shop
The server was very irl money based. and one of my suggestions is to have a 2% chance (or lower) to get a random rank from the highest tier key. Also have it so you can use any kit from a rank lower then yours.
Another suggestion is to be able to get a stack of hoppers for 5$ (if hoppers are as expensive as they used to be)
the size and the resets *CRUCIAL*
A thing i noticed that the old server had problems with, was the amount of resets. And I think it was because of the tiny world borders.
There ended up being about a reset per month in the end before the server died.
I think to avoid that problem we need a large worldborder. (not necessarily huge, but large enough for a reset to take at least 3 months.) at least 50K/50K (nether maxed out.)
Also having the end be a complete no-building zone is a bad idea also. (perhaps the entire main island is one and then there's a gateway to get away from it.) either way the end is now a very valuable dimension and should not be ignored.
HATE ME ALL YOU WANT! 1.9 PvP IS more balanced and fair. Now, I know it's hard to get used to for people who still haven't learned how to use it yet. maybe put a sign saying to enable your attack indicator in video settings. I'm a terrible fast clicker and I feel like it's better for people to get to know how to use it anyways. Sooner or later it's going to be inevitable.
I feel like spawners were the main thing that had no real problems. However I feel that them requiring silk touch was a bit of an annoyance maybe sell silk touch books at the shop. (or a custom spawner-miner enchant.
I feel like mining should have bonuses (and more than just a spawner every billion blocks) maybe diamonds are worth a lot? (obvs with good xray prevention)
I really don't want this server to die and these are things I feel like could help it keep me interesting. I don't expect all of these to be added (although I would like them to be.) and obviously some people disagree with me and I will try to respect that.